Walking Impairment Questionnaire and Walking Tests are Reliable Indicators of Success of Treatment of Peripheral Artery Disease

Abstract

The functional capacity of patients with peripheral arterial disease (PAD) represents an important indicator of patient health and quality of life. The aim of this prospective study was to investigate the validity of a walking impairment questionnaire (WIQ) compared with walking tests for the estimation of the therapeutic effect of lower limb revascularization. The study included 36 patients with PAD in whom successful percutaneous revascularization of a lower limb was performed due to disabling intermittent claudication. Before the revascularization procedure and 4–6 weeks after successful revascularization, clinical examination, ankle brachial index (ABI) measurement, 6-min walk test, treadmill test, and WIQ were performed. After revascularization, significant improvement in walking capacity was shown by both 6-min walk test and treadmill exercise test as well as with WIQ. However, the increase in ABI was borderline. Significant correlations between improvement of 6-min walk test and treadmill exercise test results and the sum of WIQ points were found. The ABI was significantly correlated with treadmill maximal walking distance only. According to our results, the WIQ correlates well with walking tests and is a reliable indicator of effective revascularization of lower limb arterial occlusions, even in patients with a nonsignificant improvement of the ABI.

Keywords

percutaneous transluminal angioplasty functional capability ankle brachial index walking impairment questionnaire

Introduction

Peripheral arterial disease (PAD) carries significant morbidity and cardiovascular (CV) mortality.¹ Patients with PAD also suffer from progressive functional decline and impaired quality of life.^2,3 With progression of the disease, the risk of CV complications as well as limitations for performing different daily activities increase.⁴ Even asymptomatic patients have a greater general functional impairment, with a faster decline, than people without PAD.^5-7

Management of PAD patients includes improvement of leg symptoms and prevention of CV complications. To improve leg symptoms, smoking cessation and exercise training represent the basic therapeutic option, whereas in advanced forms of the disease, revascularization procedures are needed. In the last decades, percutaneous revascularization (PTA) represents the prevalent invasive procedure for the management of patients with disabling intermittent claudication.^8,9 For evaluation of efficacy of both non-invasive and invasive therapeutic procedures, different measurements are used. The most frequently used test for evaluation of PAD severity is the ankle brachial index (ABI).

In patients with PAD, limited ambulation severely affects their quality of life. Therefore, in addition to imaging and perfusion tests for the evaluation of therapeutic effects of endovascular revascularization, tests for the determination of patient’s functional capacity are used.^10,11 For example, different walk tests and walking impairment questionnaires (WIQs). Studies showed lack of correlation between the results of imaging or local perfusion tests and functional tests¹² and proved that exercise training or drug treatment can ameliorate functional performance without improvement of arterial flow.¹³ However, the validity of WIQs and their relationship with other functional tests in the estimation of PTA efficacy has not been definitively elucidated. Our study, therefore, aimed to investigate the validity of the WIQ in comparison with walking tests for the estimation of therapeutic effects of revascularization of lower limb arteries using PTA, with or without stenting. We also compared the results of functional tests and WIQ with the ABI.

Patients and Methods

This prospective study was performed at an outpatient ward of the Clinical Department of Vascular Diseases, University Medical Centre, Ljubljana, Slovenia. All consecutive patients with PAD presenting as disabling intermittent claudication referred for PTA of iliac, femoral, and/or popliteal arteries in the period from October 2019 to September 2020 were screened for eligibility for inclusion in the study. Inclusion criterion was stable claudication distance from 50 to 300 m. Excluded were patients with PTA of below-knee arteries solely, patients with critical limb ischemia, walking limitations due to other health conditions, such as advanced heart failure, chronic obstructive pulmonary disease, advanced kidney failure, neuromuscular disorders, and arthritis, and those who did not consent to be included in the study. Of 143 screened patients, 36 patients with technically successful revascularization procedure (8 of them with stent implantation), confirmed by angiography at the end of procedure and 24 h later using ABI, were finally included in the study. In all patients, standard anticoagulant treatment (heparin) was used and our patients did not receive statins loading before the procedure. Procedure was safe without major adverse events and none of our patients suffered contrast-induced nephropathy.

Before the revascularization procedure and 4 to 6 weeks after revascularization, clinical examination, ABI measurement, 6-min walking test, treadmill walking test, and WIQ were performed.

The primary endpoint of this study was to compare the results of WIQ, 6-min walking test, and treadmill walking test in the estimation of therapeutic effect of revascularization of lower limb arteries. The secondary endpoint was to investigate how the results of WIQ and walking tests correlate with the change in ABI measured before and after PTA.

In all initially included patients, a complete history was obtained, and a detailed clinical examination was performed before the procedure. Ankle and brachial pressure were measured, and ABI was calculated following a previously described protocol.¹⁴

Treadmill exercise testing: the treadmill load test was performed at a constant speed of 3.2 km/h and 12% of inclination.¹⁵ The results of the tests were expressed in units of distance walked up to the claudication pain (initial claudication distance) and the maximally tolerated claudication pain (maximal claudication distance). To exclude the training effect of treadmill, testing test was performed only once before and once after the procedure. However, before testing, patients were given detailed instructions.

6-minute walk test was conducted in a 50 m long corridor following the previously described protocol.¹⁶ Patients were instructed to complete as many laps as possible. Individual stops were allowed during the test if claudication pain became intolerable, but the clock was not stopped during this time. Patients who stopped walking due to claudication pain were instructed to continue walking as soon as pain decreased. At the end of 6 min, a total walking distance was calculated. Patients were not trained to perform walk tests—they only performed the test twice, once before and once after the revascularization procedure.

Walking impairment questionnaire¹⁷—a modified WIQ, which was created at the University of Colorado Health Science Centre and modified by Coyne and co-workers,¹⁸ was used. The questionnaire was translated to Slovenian language. Four categories of walking disability were checked: pain or aching during walking in the last week, gradation of symptoms during walking up to 1000 m, difficulties to walk with different speeds, and difficulties related to climbing the stairs. Each category of walking capability consisted of 2 to 7 (altogether 16) symptoms related to the movement. Each symptom was graded from 1 to 5 points, where 1 point means that the patient had no difficulty to perform the exercise, and 5 points categorized patients who were not able to perform the exercise. If a patient collected altogether 16 points in all 16 categories (16 × 1), it indicated that he/she had no difficulties related to walking, and if a participant had 80 points (16 × 5), it meant that he/she was unable to do any type of walking. Patients who collected ≥50 points were categorized as having heavily restricted mobility.

Before inclusion in the study, all participants were informed about the study methods and provided written informed consent. The study was approved by the National Medical Ethics Committee (67-2019-4), and principles outlined in the Declaration of Helsinki were followed.

Statistical Analysis

Non-parametric values were expressed as median (interquartile range) or number (percentage). In basic comparative statistics, we applied chi-square test or 2-sided Fisher exact test and Mann–Whitney U test. Pearson correlation analysis was used in the statistical evaluation of the relationship between various parameters. A 2-sided P-value ≤.05 was considered significant. Analyses were carried out using SPSS for Windows, version 26 (IBM Corp., Armonk, N.Y., USA).

Results

The study included 36 patients in whom successful PTA due to intermittent claudication was performed. The demographic data are presented in Table 1. Most patients had ≥1 risk factor(s) for atherosclerosis, the majority of them were smokers or former smokers. Before revascularization procedure, patients had short stable claudication distance, medium value 130 m. Table 2 shows the location of arterial occlusions of lower limbs, which were treated with PTA. Most frequently superficial femoral artery (SFA) was treated (in 15 out of 36 patients; in 4 of them, both SFA were recanalized). Out of 19 procedures in the SFA, there were 12 due to significant stenosis and 7 due to total occlusion with lengths up to 10 cm. In iliac arteries, out of 15 lesions there were 7 stenoses and 8 short occlusions. In popliteal arteries, mostly stenoses (4/6) were treated. Stent was implanted in 8 patients (22.2%), 6 of them in iliac arteries, and 2 in the SFA.

Table 1.

Demographic Characteristics of PAD Patients with Intermittent Claudication Included in the Study. The Values are Reported as Median (Interquartile Range) or Number (Percentage).

Characteristic	n = 36
Gender (male)	29 (80.7)
Age (years)	68 (51-82)
Cardiovascular risk factors
Arterial hypertension^a	19 (53.8)
Hyperlipidemia^b	22 (61.5)
Active smoker	17 (46.2)
Former smoker	11 (30.8)
Never smoked	8 (23.1)
Coronary artery disease	7 (19.2)
Cerebrovascular disease	4 (11.1)

PAD: peripheral arterial disease. n: number.

^aBlood pressure >140/90 mmHg or treated hypertension.

^bLDL-cholesterol ≥2.5 mmol/L with or without treatment.

Table 2.

Clinical Characteristics of Patients with Intermittent Claudication and Location of Arterial Occlusion, which were Treated with PTA with or Without Stenting. The Values are Reported as Median (Interquartile Range) or Number (Percentage).

Characteristic	n = 36
Duration of disease (years)	2 (1-5)
Claudication distance (m)^a	130 (50-300)
Location of arterial obstructive lesions
Single SFA	11 (30.5)
Both SFA	4 (11.1)
Common IA	6 (16.7)
External IA	9 (25.0)
Popliteal artery	6 (16.7)

n: number. SFA: superficial femoral artery; IA: iliac artery; PTA: percutaneous transluminal angioplasty.

^aData from history before treatment.

The results of functional tests, ABI, and WIQ before and after revascularization procedures are shown in Table 3. The patients’ history as well as the results of the treadmill test showed that before treatment, the participants had on average a short claudication distance, ABI between .55 and .66 and the sum of points of the WIQ was 62, all of which indicated that most of the patients had severely restricted mobility. After intervention, all investigated indicators of functional capability as well as the ABI significantly improved. The extent of improvement was greater in WIQ and some of the walking tests. The distance of the 6-min walk test before, and particularly after treatment, was significantly longer than the distance that patients were able to walk on the treadmill.

Table 3.

Results of Functional Capacity: Walk Tests, Walking Impartment Questionnaire, and ABI Before and After Intervention (PTA with or Without Stenting) Performed in Patients with PAD. The Values are Reported as Median (Interquartile Range or Percentage).

	Before intervention n = 36	After intervention n = 36	P
Claudication distance (history)(m)	120 (50-300)	300 (100-1000)	<.001
Treadmill test (m)
Initial claudication distance (m)	53 (26-153)	100 (15-530)	<.001
Maximal claudication distance (m)	106 (36-165)	212 (50-530)	<.001
6-min walk test (m)	327 (274-415	578 (423-705)	<.001
ABI	.62 (.31-.82)	.78 (.42-1.1)	<.047
Sum of points with WIQ	62 (40-76)	34 (16-62)	<.001

ABI: ankle brachial index; WIQ: walking impairment questionnaire; PAD: peripheral arterial disease; PTA: percutaneous transluminal angioplasty P < .05 is significant.

The analysis of individual patients’ response to treatment showed that in 4 out of 36 patients with technically successful recanalization of the SFA, functional capacity did not improve significantly. In 3 patients with successful reopening of occluded SFA, the ABI did not increase significantly.

Walking tests, particularly the 6-min walk test and WIQ, showed improvement of walking capability.

Table 4 shows a relationship between the differences in the values of ABI, walk tests and WIQ before and after endovascular treatment as a measure of therapeutic effects. Significant correlations were found in claudication distance from the patient’s history with a treadmill claudication distance (initial and maximal), 6-min walk test, and walking capacity estimated by WIQ. The sum of WIQ points was inversely correlated with all walk tests: 6-min walk test (r = - .573, P < .015), treadmill initial claudication distance (r = .427, P = .033), and treadmill maximal distance (r = - .528, P = .007), as well as the claudication distance reported by patient’s history (r = - .433, P = .001). However, the ABI was significantly correlated only with treadmill maximal walking distance, while borderline correlations were found between ABI and claudication distance from patient’s history, 6-min walk test, and WIQ.

Table 4.

Correlation Between the Differences in Values of Ankle Brachial Index (ABI), Walk Tests, and Walking Impairment Questionnaire (WIQ) Before and After Treatment (Extent of Improvement).

	Claudication distance (history)	6-min walk test	Treadmill walking test: Initial walking distance	Treadmill walking test: Maximal walking distance	Differences in ABI	WIQ
Claudication distance (history)	r = 1.00
6-min walk test	r = .456	r = 1.00
6-min walk test	P = .566	r = 1.00
Treadmill walking test: initial claudication distance	r = .355	r = .455	r = 1.00
Treadmill walking test: initial claudication distance	P = .560	P = .189	r = 1.00
Walking treadmill test: maximal claudication distance	r = .033	r = .677	r = .789	r = 1.00
Walking treadmill test: maximal claudication distance	P = .177	P = .550	P = .093	r = 1.00
Differences in ABI	R = .567	r = .765	r = .933	r = .345	r = 1.00
Differences in ABI	P = .056	P = .057	P = .277	P = .008	r = 1.00
WIQ	r = -.433	r = −.573	r = -.427	r = -.528	r =-.272	r = 1.00
WIQ	p = <.001	p = <.015	P = .033	P =.007	P = .06	r = 1.00

P < .05 is significant.

Discussion

Atherosclerosis is a chronic inflammatory disease provoked by well-known risk factors, among which smoking and diabetes represent outstandingly important risk factors for PAD.¹⁹ Therefore, healthy lifestyle and strict control of diabetes, hypertension, and dyslipidemia represent the cornerstone of management of patients with PAD. In advanced stages of PAD however, arterial recanalization is necessary to prevent amputation. After revascularization, management of atherosclerotic risk factors is important to maintain the long-term effect of revascularization. In our study, risk factors were evaluated in all patients before the procedure; medication for diabetes, arterial hypertension and dyslipidemia was optimized; and smoking cessation was recommended. The estimation of immediate therapeutic effect of revascularization is based on angiographic presentation of the treated vessel segment. However, this gives information only on technical success of the procedure. As patients with PAD, besides local symptoms related to the diseased leg, usually have limited systemic functional capacity, diagnostic tests dealing with local perfusion do not always provide insight into the patient’s functional capacity, a determinant of quality of life.^13,20

Functional limitations experienced by patients with PAD are frequently associated with decreased independence, loss of mobility, and increased mortality.⁷ Therefore, functional tests should be a part of the evaluation of treatment success in patients with PAD. Especially in the case of non-invasive treatment, like exercise training or medication, leg symptoms, and overall walking ability can substantially improve without any increase in ABI.^21,22 Improvement could be the consequence of collateral development and better perfusion of tissues distal to arterial occlusion, which cannot be detected with a test like the ABI. In contrast, walk tests enable estimation of functional capacity and its limitation which is a consequence of both local disease and related general condition of PAD patients.²³

Our study included patients with successful PTA of above the knee arteries of the lower limbs. While technical success of revascularization was confirmed by angiography at the end of the procedure, the clinical success was evaluated at follow-up investigation 4–6 weeks after the procedure with the determination of ABI, walking tests, and WIQ. In most patients (31/36), the ABI, as a surrogate endpoint of procedural success, increased by >.1.²¹

Tests for determination of functional capacity of patients with PAD and WIQ are frequently used. However, the data on their usefulness for estimation of revascularization efficacy are limited.

The ABI is usually used as a measure of revascularization success.^24,25 In our patients, the ABI on average increased by only 26%. In contrast, most of the walk tests and WIQ improved by nearly 100%. This suggests that functional tests are more sensitive indicators of the clinical benefits of revascularization of lower limbs arteries than the ABI. Furthermore, the results of our study showed that in some patients, despite successful recanalization of proximal arteries of the lower limbs, the ABI did not increase significantly, while their functional capability improved. These were patients with remaining segmental occlusions of distal (below the knee) arteries. Improvement of walking capability of these patients was most probably the consequence of opening of new collaterals and improvement of perfusion of the distal part of the leg which cannot be registered by ABI. However, psychological effects cannot be excluded.

Different walk tests have advantages and disadvantages. In patients with health problems, particularly arthritis and neuromuscular disorders, claudication distance reported by patients is not an objective indicator of limitation of walking capability. The performance of some walk tests based on special equipment, like a treadmill, is not always feasible in a clinical setting. The 6-min walk test does not demand any special equipment and is also more comfortable for patients with PAD, who have difficulties in walking, since they can slow down or even rest temporarily, and then resume walking without stopping the test. This is the key difference between the 6-min walk test and the treadmill performance. Consequently, 6-min walk test is likely to result in a longer walking distance compared with a treadmill test.¹⁶ In our study, the 6-min walk test distance was up to 3-times longer than the walking distance on treadmill. This indicates that the treadmill test requires greater patient’s effort compared with corridor walking.²⁶

The results of the 6-min walk test and its changes after revascularization treatment were significantly correlated with the results of WIQ, but not with the results of treadmill tests. Other studies also reported marginal utility of 6-min walk test in assessing the effects of interventions.²⁷

One of the studies that evaluated home-based exercise training showed that the treatment effect estimated by the treadmill test was 2.4 times greater compared with the 6-min walk test.⁶

However, in older patients with comorbidities that affect the walking ability, walking length is reduced and anxiety during treadmill walking is often present. These limitations are not present during the corridor walk tests such as a 6-min walk test.²⁶

Furthermore, studies also showed that 6-min walk test correlated much closer with the physical activity level in the community than with the treadmill testing.²⁸ The 6-min walk test is also not associated with learning effect when repeated testing is performed in patients with PAD.²⁹

A disadvantage of some functional tests is the requirement of special equipment for their performance. The data on functional and walking capacity, obtained during routine clinical examination of patients with PAD, are frequently inconsistent and unreliable, but the WIQ which assesses patient’s self-report of difficulties during every day walking and his quality of life enables more reliable insight into the patient’s ability to perform different types of movement.³⁰ In our study, the WIQ was significantly correlated with all performed walk tests, but a nonsignificant correlation was found between the WIQ and ABI. This finding indicates that the WIQ is a practical and representative measure of treatment success and represents the patient’s health-related quality of life.^18,31 The validity of the WIQ is limited by comorbid conditions, like depression and atypical symptoms of claudication.¹³ The absence of correlation between WIQ and ABI indicates that diagnostic tests investigating blood flow on the macrovascular level are less reliable indicators of patients’ functional capacity than functional tests or WIQ. Similar results were reported by Regensteiner et al.³² in this study which investigated the effect of exercise training on the functional status of PAD, a weak correlation was shown between the ABI and walking impairment evaluated by questionnaire, especially if tested in small groups of patients. Therefore, besides walk tests, the WIQ is a practical, reliable, valid, and representative measure of the functional capability in patients with intermittent claudication; it is also an easily obtained indicator of the efficacy of revascularization procedures.^13,33

In conclusion, in patients with intermittent claudication, PTA represents a treatment option particularly for patients with short claudication distance, which results in improved hemodynamics of a diseased leg. It should improve patient’s walking distance and mobility, which are important determinants of the quality of life. However, as it was shown in our and other studies, the correlation between limb hemodynamics and walking capacity in patients with PAD is surprisingly weak. Accordingly, to assess the response to therapeutic interventions, exercise performance and functional status need to be directly measured. For the investigation of functional capacity, beside the treadmill test, the 6-min walk test is an attractive way to assess mobility. It is simple to perform and requires minimal equipment. Recently, it was shown that beside the classical walk tests, the WIQ represents a useful technique for the investigation of functional capacity in patients with PAD. The results of our study showed a close relationship in therapeutic response assessment between WIQ and other functional tests. The WIQ estimates different types of patient’s mobility and enables a longer period of observation. Therefore, it could be routinely used as diagnostic tool for the estimation of functional capacity and effects of treatment, including revascularization procedures.

Limitations of the Study

The study included small number of patients. It is a single-center study and because of the strict inclusion and exclusion criteria, a limited number of eligible patients were identified in the screening period of 1 year. Further, 7 out of 43 patients refused participation in the study. To avoid learning effect, treadmill test as well as 6-min walk test were performed without training. This could influence the objectiveness of the results.

The idea of “training” is to ensure that you have achieved the maximum performance of the patient and that he/she cannot increase it any further. In other words, a patient who is now familiar with the test and who is trying to improve his/her past performance is likely to do better. Unfortunately, the second test will suffer that potential bias.

Footnotes

Author Contributions

All authors contributed to: (1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data, (2) drafting the article or revising it critically for important intellectual content, and (3) final approval of the version to be published.

Declaration of Conflicting Interest

The authors declare that they have no conflict of interest.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Pavel Poredos

Peter Poredos

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